Are MATLAB built-in function scripts editable?

Hi,

I have some questions with MATLAB function scripts.

First, how can I know which .m script file under C:\Program Files\MATLAB\ corresponds to the function being executed? For example, randn().

Second, if I search for “randn” under C:\Program Files\MATLAB\, there are four files under four different folders:

(1) C:\Program Files\MATLAB\R2008a\toolbox\compiler\mcr\matlab\elmat Empty

(2) C:\Program Files\MATLAB\R2008a\toolbox\matlab\elmat\ja Invalid text

(3) C:\Program Files\MATLAB\R2008a\toolbox\eml\lib\matlab\elmat valid text, code

(4) C:\Program Files\MATLAB\R2008a\toolbox\matlab\elmat valid text, help

(4) seems to be the help document which is shown after typing “help randn” in the command window, and any change (with Administrator account which has no access restriction) in its contents will be reflected when typing “help randn” again.

However, changing (3) (with Administrator account which has no access restriction) has no effect and command window commands or text editor scripts including randn() still executes normally.

So I guess MATLAB has compiled code of .m scripts stored elsewhere and actually executes them when a function is being called, so that even if the users deletes all .m codes, all related functions could still be executed normally?

This seems also prevents the user from modifying the default behavior of built-in function; if I want a slightly-modified version of built-in functions, then I need to copy it to a new location, modify its content, change its name, and then add the new location to the search folder or set as current folder. Is this correct?

Bob

Answer 1

[Walter Roberson]

which -all randn

For me it shows

built-in (/opt/matlab7_ng/toolbox/matlab/randfun/randn)
/opt/matlab7_ng/toolbox/matlab/randfun/@RandStream/randn.mexa64  % RandStream method
/opt/matlab7_ng/toolbox/matlab/randfun/@RandStream/randn.m       % RandStream method

There is no .m corresponding to built-in functions, and the randn.m only contains the help information for the binary randn.mexa64 that has priority.

toolbox\eml is Embedded MATLAB, which is not the randn normally used.

If you want a slightly modified version of the built-in functions, put the modified version earlier on the path (still dangerous as other routines might pick it up); or use OOP and class methods so that your modified version is only used in restricted circumstances. Renaming and so on is a very good idea.

If something shows up as built-in then you are not likely to be able to get the source for it (at least not their source.) (There are a few exceptions, a few packages for which C or C++ code is provided.)

[Bob Li]

Walter,

First question:

If the original code of built-in functions cannot be found, how to modify them?

Second questions:

I searched C:\Program Files\MATLAB\R2008a\ for *.mexa* (* as wildcard), but there was no results at all? You example was "randn.mexa64", but on my 32-bit PC I removed 64, but wildcard "*" would include it. Why there is no result?

Are your .mexa64 intended to be compiled files? Are they intermediate code like p-code, or more close to PC's machine code?

Bob

[Walter Roberson]

If you need to modify the original code of the built-in functions, then you need to get a job with MathWorks. (I am not being funny about that: that is MathWork's response.)

The which -all should show the appropriate file extension for you. It is probably w32 . See http://www.mathworks.com/help/techdoc/matlab_external/f29502.html#bra56dy-1

.mex* are (host) compiled C or Fortran. They can use whatever operating system calls are available on the platform. They can operate independently, and they can make calls in MATLAB routines. They are not intermediate code.

[Wayne King]

@Walter I think in the OP's version, it just says built-in for randn. In more recent versions, it shows up as a mex file in the @RandStream directory.

[Walter Roberson]

Good catch, Wayne, I happen to be running R2008b, the first version that had RandStream, whereas the OP is running R2008a, the last version without.

Bob: You are probably defaulting to what was then called 'twister', which is Mersenne Twister mt19937ar, the source for which is available through http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html

The one difference that I know of is that MATLAB rejects 0 as an outcome (and, I gather, generates again). This rejection has some useful properties in practice.

[Bob Li]

Wayne,

I googled Mathworks.com for "OP" but didn't find useful results. What do you mean by "OP"?

Bob

[Bob Li]

Walter,

I think I understand your answers now. Thanks very much.

Bob

[Titus Edelhofer]

OP stands for Original Poster ...